Presently there are known various types of by-pass vacuum motors. Typically, such motors have several air paths, the working air path being separate from the motor cooling air path, such that affluent does not reach the motor assembly itself. Having several air paths, necessarily generated by separate fans, the generation of noise is of concern in such units. Conventional by-pass vacuum motors generate a large siren-like noise component due to the proximity of the exhaust louver ports to the high speed rotating fan blade passing thereby. The noise is generated by the attendant pressure pulses characterizing the working air. As is known, the noise frequency is dependent upon motor speed, the number of fan blades per fan, and the number and proximity of stationary objects such as louvers or exhaust ports. There is also a broad band noise component resulting from the vortex and turbulence of the air as it leaves the rotating fan.
While the prior art design of by-pass vacuum motors has been conducive to ease of manufacture of an efficiently operating system, such has been at the expense of audible noise. While noise is typically objectionable in any environment, the use of such motors in hospitals, rest homes, and the like dictates that the noise level be significantly reduced. In the past, to reduce sound, substantial amounts of sound absorbing material and/or labyrinthing have been added to the vacuum cleaner or other device requiring the by-pass type vacuum motor, all at the expense of material, labor, and physical size. Additionally, such structures have often been found to reduce motor efficiency.